The present invention relates to a reflector drive mechanism applicable to a headlamp system of so called a variable light distribution type headlamp which, when an automobile is running in a winding road, deflects the illuminating light of the headlamp to a side toward which the automobile is going to turn.
There has been demand for a headlamp for use in an automobile which, when the automobile is running on a winding road, is capable of deflecting the illuminating light of the headlamp to a side toward which it is going to turn in accordance with the angle of rotation of a steering wheel to thereby secure a good visibility in a road ahead. Thus, conventionally, there has been used a variable light distribution type headlamp using a projection lamp, as shown in FIG. 1.
In other words, in the above-mentioned conventional variable light distribution type headlamp, a bulb 51 serving as a light source is disposed at a first focal point F1 of a reflector 50 consisting of an ellipsoidal reflecting mirror surface and having an optical axis L, a collimator lens 52 having the optical axis L in common with the reflector 50 is fixedly disposed in front of the optical axis L of the reflector 50 with the focal point of the lens 52 substantially identical with a second focal point F2, and a shade 53 pivotally disposed at the position of the second focal point F2 and extending across the optical axis L can be driven or displaced by an actuator such as a motor 54 or the like, that is, the shade 53 can be turned (in a direction of an arrow A shown in FIG. 1) by means of the motor 54 so that the shade 53 corresponds to the angle of rotation of a steering wheel of an automobile. That is, by changing the cut-off position of the illuminating light by the shade 53, the light distribution pattern of the illuminating light is controlled so as to match the running direction of the automobile.
However, in the conventional variable light distribution type headlamp, due to the fact that the illuminating light of the headlamp is previously diffused so as to correspond to the angles of the headlamp when the headlamp is swung right and left and the illuminating light is cut off by the shade 53 to thereby obtain a necessary light pattern, the amount of the light to be cut off is large and the thermal efficiency is poor so that the amount of light of the bulb 51 serving as the light source must be large. As a result of this, not only there arise economical disadvantages due to the poor thermal efficiency and due to use of the large bulb 51, but also there is required a countermeasure on the heat storage of the headlamp.
Also, in the above-mentioned conventional structure, in addition to the problem of heat storage in the headlamp, since a drive mechanism serving as a drive mechanism portion of the shade 53 must be disposed within the headlamp, there arises a further problem in heat. Further, in the conventional structure, since the light is cut off by the shade 53 to thereby form an illuminating pattern, only the two-dimension change on the optical axis L of the shade 53 can be reflected on the pattern change, with the result that the light swung right or left provides a dazzling light against an oncoming automobile.
In addition, in the above-mentioned variable light distribution type headlamp, the illumination distribution of the illuminating light depends on the projection of the illumination distribution on the focal plane of the collimator lens, with the result that the illumination distribution of the illuminating light is influenced by the distribution condition of the light on the focal plane to be collected by the reflector. Therefore, in the structure of the above-mentioned variable light distribution type headlamp, when the optical arrangement of the collimator lens and shade is fixed, the shape of the cut-off line in the pattern of the illuminating light can be maintained however, if the optical arrangement of the reflector with respect to the shade is changed, then the illumination distribution of the cut-off line is caused to vary. In other words, if the reflector is displaced along the optical axis thereof, then the light collecting condition of the illuminating light is caused to vary. Also, if the reflector is displaced in a direction perpendicular to the optical axis, then the illumination pattern is changed in the opposite direction.